From d4f03f0daf29488f4e96af2618285bde8f768a13 Mon Sep 17 00:00:00 2001
From: Andy Gocke <andy@commentout.net>
Date: Wed, 28 Jun 2023 13:00:04 -0700
Subject: [PATCH] Fix scope overlapping in NAOT DWARF info

We currently create a new lexical scope for each live variable
range as reported by the JIT. Liveness ranges, however, are
not the same as lexical scopes. In particular, lexical scopes
are never partially overlapping. Liveness ranges are. Overlapping
scopes produce errors in llvm-dwarfdump --verify. This change maps
the objwriter behavior to use one lexical scope for the whole method,
which is the semantic used in IL. This is overly broad, but correct
according to the DWARF spec. We can add support for proper lexical
scopes using the PDB information in the future.
---
 .../objwriter/debugInfo/dwarf/dwarfGen.cpp    | 77 ++-----------------
 1 file changed, 6 insertions(+), 71 deletions(-)

diff --git a/llvm/tools/objwriter/debugInfo/dwarf/dwarfGen.cpp b/llvm/tools/objwriter/debugInfo/dwarf/dwarfGen.cpp
index 033a8f1954dcb..207a1956384a5 100644
--- a/llvm/tools/objwriter/debugInfo/dwarf/dwarfGen.cpp
+++ b/llvm/tools/objwriter/debugInfo/dwarf/dwarfGen.cpp
@@ -492,19 +492,10 @@ static void EmitVarLocation(MCObjectStreamer *Streamer,
 class LexicalScope
 {
 public:
-  LexicalScope(uint64_t Start, uint64_t End, bool IsFuncScope = false) :
-               Start(Start),
-               End(End),
-               IsFuncScope(IsFuncScope) {}
-
-  LexicalScope(VarInfo *Info) :
-               Start(Info->GetStartOffset()),
-               End(Info->GetEndOffset()),
-               IsFuncScope(false) { Vars.push_back(Info); }
-
-  bool IsContains(const VarInfo *Info) const {
-    return Start <= Info->GetStartOffset() && End >= Info->GetEndOffset();
-  }
+  /// At the moment, the lexical scope reflects IL, not C#, meaning that
+  /// there is only one scope for the whole method. We could be more precise
+  /// in the future by pulling the scope information from the PDB.
+  LexicalScope() {}
 
   void AddVar(VarInfo *Info);
 
@@ -512,76 +503,20 @@ class LexicalScope
       MCSection *TypeSection, MCSection *StrSection, const MCExpr *SymExpr);
 
 private:
-  uint64_t Start;
-  uint64_t End;
-  bool IsFuncScope;
   std::vector<VarInfo*> Vars;
-  std::vector<LexicalScope> InnerScopes;
 };
 
 void LexicalScope::AddVar(VarInfo *Info) {
-  if (Info->IsParam() && IsFuncScope) {
-    Vars.push_back(Info);
-    return;
-  }
-
-  if (!IsContains(Info))
-    return;
-
-  uint64_t VarStart = Info->GetStartOffset();
-  uint64_t VarEnd = Info->GetEndOffset();
-
-  // Var belongs to inner scope
-  if (VarStart != Start || VarEnd != End) {
-    // Try to add variable to one the inner scopes
-    for (auto &Scope : InnerScopes) {
-      if (Scope.IsContains(Info)) {
-        Scope.AddVar(Info);
-        return;
-      }
-    }
-    // We need to create new inner scope for this var
-    InnerScopes.emplace_back(Info);
-  } else {
-    Vars.push_back(Info);
-  }
+  Vars.push_back(Info);
 }
 
 void LexicalScope::Dump(UserDefinedDwarfTypesBuilder *TypeBuilder, MCObjectStreamer *Streamer,
       MCSection *TypeSection, MCSection *StrSection, const MCExpr *SymExpr) {
   Streamer->SwitchSection(TypeSection);
 
-  if (!IsFuncScope)
-  {
-      // Dump lexical block DIE
-      MCContext &context = Streamer->getContext();
-      unsigned TargetPointerSize = context.getAsmInfo()->getCodePointerSize();
-
-      // Abbrev Number
-      Streamer->emitULEB128IntValue(DwarfAbbrev::LexicalBlock);
-
-      // DW_AT_low_pc
-      const MCExpr *StartExpr = MCConstantExpr::create(Start, context);
-      const MCExpr *LowPcExpr = MCBinaryExpr::create(MCBinaryExpr::Add, SymExpr,
-          StartExpr, context);
-      Streamer->emitValue(LowPcExpr, TargetPointerSize);
-
-      // DW_AT_high_pc
-      Streamer->emitIntValue(End - Start, TargetPointerSize);
-  }
-
   for (auto *Var : Vars) {
     Var->Dump(TypeBuilder, Streamer, TypeSection, StrSection);
   }
-
-  for (auto &Scope : InnerScopes) {
-    Scope.Dump(TypeBuilder, Streamer, TypeSection, StrSection, SymExpr);
-  }
-
-  if (!IsFuncScope) {
-    // Terminate block
-    Streamer->emitIntValue(0, 1);
-  }
 }
 
 // StaticVarInfo
@@ -855,7 +790,7 @@ void SubprogramInfo::DumpVars(UserDefinedDwarfTypesBuilder *TypeBuilder, MCObjec
   MCSymbol *Sym = context.getOrCreateSymbol(Twine(Name));
   const MCExpr *SymExpr = MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_None, context);
 
-  LexicalScope FuncScope(0, Size, true);
+  LexicalScope FuncScope;
 
   for (unsigned i = 0; i < VarInfos.size(); i++) {
     FuncScope.AddVar(&VarInfos[i]);